>You will never make it to our shores.
The USA has bases all around the world. The sun never sets on USA bases. Any invading force would be encircled before it could get its boats/planes en route.
But if an invading army in uniforms did make to the mainland, there would be a gun behind every blade of grass. The bigger threat is an invading army of guerrillas who don't wear uniforms and who might arouse misguided sympathy if they were shot on sight.